This invention relates to an opening and closing device for the opening at the front end of a rectractable nib fountain pen.
Heretofore, it has been known to provide an elastic portion at the front end of a retractable fountain pen in order to prevent drying of ink at the pen point. A sealing effect is produced utilizing the elastic deformation of the elastic member at an abutment.
Japanese Utility Model Publn. No. 82/1967 are typical of such devices. The Japanese publication discloses that an elastic ring having a communicating hole communicating with a throughhole of the holder and a tapered front end at which the connunicating hole is opened is connected to the holder. A cover plate is usually biased towards the tapered front end by means of a spring action to close the communicating hole of the elastic ring. The elastic ring utilized has a cross secion of equal thickness throughtout and is of short length.
However, such a construction has, in practice, caused various problems. Namely, in retractable fountain pens, writing is effectuated by projecting the pen out from the holder. In this case, however, since the projecting of the pen is carried out by pushing the cover plate with the tip point of the pen, the strength of the spring is limited in order to prevent damage and deformation of the pen point. Accordingly, in order to prevent ink drying at the pen point by perfectly mating the cover plate against the elastic ring having the shape described above, it is inevitable that the elastic ring will be made of a material having sufficient elasticity. Alternatively, the thickness of the elastic ring itself will be reduced since the strength of the spring is limited as described above. In this case, however, when the elastic ring is prepared using a material having sufficient elasticity, since the elastic ring itself is of short length, it is liable to be deformed and would be strained. On the other hand, if the thickness of the elastic ring is reduced, buckling is produced due to excess bending at the abutment with the cover plate. Such a strain, or excessive bending or buckling, produces a partial gap between the elastic ring and the cover plate so that no effective seal is made, making it difficult to prevent the drying of ink at the pen point.